This invention relates generally to a gear pump. More particularly it relates to a bi-directional gear pump having advanced porting. The pump is of the type incorporating a gerotor gear set wherein internally and externally toothed members cooperate to define successively expanding and contracting fluid cavities during rotation of the members on spaced parallel axes. Fluid flows into expanding cavities and out of contracting cavities through inlet and outlet ports communicating with a chamber in which the members are rotatably mounted.
In such a pump, noise and a fall-off in pump delivery are caused by cavitation. This problem can become excessive where the pump is operated at high speeds, such as in an automotive, marine or industrial application.
One way of eliminating cavitation is by the use of advanced porting. In the typical prior art pump, the inlet port was lengthened and the outlet port shortened (FIG. 2). This extended the time during which each pump cavity was allowed to fill. It also permitted the largest cavity in the pump to begin decreasing in volume while still in fluid communication with the inlet port.
One disadvantage of advanced porting was that it could not be incorporated in a bi-directional pump. This was so because the typical prior art pump required rotation of the hydraulic centerline by 180.degree. when the direction of pump rotation was to be reversed. In order to provide a bi-directional capability, the ports should be symmetrical about a line (line X in FIG. 3) which is perpendicular to the port centerline. Since advanced porting (FIG. 2) did not provide this symmetry, it could not heretofore be incorporated in a bi-directional pump.
Thus, there remains a need in the art for an internal/external gear pump which is bi-directional and which includes the advantages of advanced porting.